Research Article Numerical Analysis on Failure Modes and Mechanisms of Mine Pillars under Shear Loading Tianhui Ma, 1,2 Long Wang, 1 Fidelis Tawiah Suorineni, 2 and Chunan Tang 1 1 State Key Laboratory of Coastal and Ofshore Engineering, Dalian University of Technology, Dalian 116024, China 2 School of Mining Engineering, Faculty of Engineering, UNSW Australia, Sydney, NSW 2051, Australia Correspondence should be addressed to Tianhui Ma; tianhuima@dlut.edu.cn Received 13 January 2016; Accepted 11 April 2016 Academic Editor: Marcin A. Luty´ nski Copyright © 2016 Tianhui Ma et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Severe damage occurs frequently in mine pillars subjected to shear stresses. Te empirical design charts or formulas for mine pillars are not applicable to orebodies under shear. In this paper, the failure process of pillars under shear stresses was investigated by numerical simulations using the rock failure process analysis (RFPA) 2D sofware. Te numerical simulation results indicate that the strength of mine pillars and the corresponding failure mode vary with diferent width-to-height ratios and dip angles. With increasing dip angle, stress concentration frst occurs at the intersection between the pillar and the roof, leading to formation of microcracks. Damage gradually develops from the surface to the core of the pillar. Te damage process is tracked with acoustic emission monitoring. Te study in this paper can provide an efective means for understanding the failure mechanism, planning, and design of mine pillars. 1. Introduction Studies on pillar size and stability have been conducted for many years. Te main research methods include the safety factor, probabilistic analysis, numerical modeling, empirical methods, and physical testing methods. Brady et al. [1] developed a pillar strength formula accounting for pillar size and geometry based on the existing representative design theory for pillar spacing. Bieniawski [2] considered that the compressive strength of coal cubes (short-term strength) decreases with an increase in size and reaches an asymptotic value at a cube size of about 1.5 m which, according to him, was the critical size for coal. Lunder and Pakalnis [3] considered the role of confnement in hard rock pillar strength. Gonz´ alez-Nicieza et al. [4] proposed a new formula considering Bieniawski’s rock mass quality classifcation and the shear-resistance safety factor of pillars. Esterhuizen [5] investigated some of the issues afecting pillar strength at low width-to-height ratios in hard brittle rock and concluded that the strength of slender pillars was more variable than that of wider pillars. Mortazavi et al. [6] suggested that, at high WH ratios, pillars behave in a very stif manner in the elastic range, demonstrating a high load-bearing capacity. Esterhuizen et al. [7] developed a pillar strength equation based on stable and failed pillars observed. Ghasemi and Shahriar [8] proposed a new coal pillar design method. Suorineni et al. [9, 10] developed new knowledge on why pillars in ore bodies in shear are more prone to catastrophic failures than would normally be expected. Tey introduced the concept of shear loading in orebodies and pillars. Many scholars in China have carried out in-depth studies on pillar stability. Liu and Xu [11] estimated rock mass strength for the gob area of a phosphate mine according to rock mass classifcation, analyzed stability of pillars in the gob area using the safety factor and reliability analysis methods, and represented the safety factor of pillars by the average safety factor. Yang [12] proposed a new design method for pillar spacing, which has been applied efectively in engineering practice. Wang and Li [13] proposed the concept of shear-resistance safety factor for mine pillars, considering that pillars generally fail in shear. Tey suggested that pillars were safe and reliable when the shear-resistance safety factor was greater than 1.2. Wang et al. [14] proposed a formula for pillar width for deep stope mining and suggested Hindawi Publishing Corporation Shock and Vibration Volume 2016, Article ID 6195482, 14 pages http://dx.doi.org/10.1155/2016/6195482